Another day, another new idea for what dark matter might be. This time, it is a paper that proposes dark matter is made of regular matter. For those who are familiar with dark matter, this might raise an eyebrow because dark matter can’t be regular matter. In fact, what this paper shows is that while observational data excludes the usual suspects for dark matter such as cold gas and dust, small black holes and the like, there might be a way to shoehorn regular matter into the picture. The solution they propose is, quite literally, a bit strange.

The global positioning system (GPS) is an array of satellites orbiting the Earth, which can be used to pinpoint your location. Each of the satellites transmits a signal with its current position and time. A GPS receiver can then use signals from multiple satellites to determine where it is on the planet. GPS is perhaps most widely used in mobile phones. If you’ve ever had your phone give you directions, you’ve used GPS. In order to work properly, the clocks on a GPS satellite need to be extraordinarily precise. So precise that the effects of special and general relativity must be taken into account.